The recovery of caffeine from decaffeinating solvents has been an active area of concern for many years. For example, in U.S. Pat. No. 2,508,545, Shuman discloses that activated carbon and other adsorbents had been used to remove impurities from solutions of caffeine extracted from coffee. Shuman indicates that until the time of his invention caffeine losses due to adsorption onto the carbon ran as high as 10 to 14%. To rectify this, Shuman disclosed alternate use of organic and aqueous extractions with the final aqueous extraction being done at a pH of at least 7. While activated carbon is employed to remove impurities from the aqueous extract, the amounts employed are apparently small and no mention of separating caffeine from the carbon is made. Similarly, in U.S. Pat. No. 2,472,881, Bender employs activated carbon to remove impurities from an aqueous caffeine solution but does not discuss the steps taken to recover the caffeine adsorbed on the carbon.
Recently, an improved decaffeination method was disclosed in U.S. Pat. No. 3,879,569 wherein quantitative extraction of caffeine from raw coffee beans is achieved with moist supercritical carbon dioxide. This process produces an extract from which essentially all of the caffeine can be removed by activated carbon. Unfortunately, the prior art techniques do not economically provide good levels of recovery of caffeine or they require the use of chlorinated hydrocarbon solvents which are otherwise avoided by the use of carbon dioxide as an extractant.